Spatial focusing of ions was used in field of mass spectrometry, which avoids the difference of flight time for the same ions with different velocity due to their initial different position and potential. Evident increase of resolution of mass spectrometry was achieved with the use of spatial focusing technique.
The focusing of ion in mass spectrometry was realized in vacuum where ions fly under the actions of acceleration of electrical field and inertia. Thus, the energy loss of ions could be negligible due to the low possibility of collisions with other particles. However, ion mobility spectrometry separates the different ions at atmospheric pressure. The electric field was used to overcome the obstruction due to the collision of ions with molecules of drift gas. To realize the focusing of ions at atmospheric pressure, a non-uniform electric field (∂E/∂d≠0) is essential in initial conditions, which makes the lagged ions obtain higher velocity and pursue the front ions at the beginning. Thus, the focusing of ion was realized.
The spatial focusing of ion under atmospheric pressure was realized in high-field asymmetric waveform ion mobility spectrometry, which separate different ions based on the different mobility between high-field portion and low-field portion of the waveform. Spatial focusing is achieved in high-field asymmetric waveform ion mobility spectrometry with cylindrical structure based on the amplitude variation of drift length of ions in radial positions in the separation space.
As far as we know, there is no report about the focusing linear drift tube ion mobility spectrometry. For the first time this invention introduced the linear drift tube ion mobility spectrometry with the function of focusing. The spatial focusing of ions is achieved using a non-uniform electric field based a simple structure and was verified with experimental results.